Question

what is the lengthof a hypotenuse of the right triangle ABC in the figure

Answer 1

there is no figure. 
but you can use A^2 + B^2 = C^2
C is your hypotenuse. 
so if you have the other two lengths if you square them and add them you'll have C squared. So you'll have to find the square root of that number to actually find the length.